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7
EQ2-UM-1.3
in Fig. 3, in both the wetting and drying phases the time lag is similar to that for transducer
tensiometers.
Table 1: Hysteresis of the
Equitensiometer
in a rapid drying test. The values are much
higher than under natural conditions.
Matric potential, absolute changes
kPa kPa/min
Errors in kPa after minutes
0 10 30 60 120 180 300 360
-98
-.11
2.2
0.3
0
0
0
0
0
0
-215
-.15
5.6
5.3
2.6
0
0
0
0
0
-376
-.37
20.2
19.1
18.0
16.2
13.5
10.1
3.4
0
Soil properties and salinity
The
Equitensiometer
is unaffected (not damaged) by physical soil properties (organic
matter, stones, bulk density,) and most chemical soil properties (e.g. pH). No tests have
been carried out in saline soils, so the performance of the
Equitensiometer
in saline soils is
unknown.
Temperature
The output of the
Equitensiometer
is slightly dependent on temperature. The Calibration
certificate gives values correct at 20°C. For regions with strong temperature variations, the
following temperature correction should be applied.
( )
( )
( )
ù
êë
é
−
°
−
=
4
20
_
_
C
e
temperatur
mV
value
measured
mV
value
Corrected
The
Equitensiometer
will not be damaged by frost, but its sensitivity to ice is very much
less than water, so any measurements taken below freezing will be meaningless.
Maintenance
Large concentrations of Sodium ions may affect the calibration curves. If the equilibrium
body becomes contaminated, the sodium may be washed out by repeatedly wetting it in de-
ionised water, and then drying it out by inserting it into dry non-saline soil. Washing with
water does not help, because in that case no exchange of water or solute takes place.
The calibration should be stable for ~2 years. It can be checked by putting the probe into
de-ionised water and checking the reading against the 0 kPa value in its calibration table -
at 20°C the reading should be within ± 20 mV. If re-calibration is required the probe will
need to be returned to Delta-T Devices.
No other maintenance is required.
